Humanized mouse model of periodontitis

This application for R21 grant, entitled, “Humanized mouse model of periodontitis”, proposes to develop a humanized mouse model of periodontitis to study the possible pathogenic roles of Semaphorin 4D (Sema4D) expressed on human osteoclasts in periodontitis lesion. NSG-SGM3-W41 mouse strain which is one of the most advanced immunodeficient mouse strains developed by Dr. Shultz at the Jackson Laboratory allows to reconstruct the full immune compartments containing both myeloid and lymphoid cell populations following transplantation of human hematopoietic stem cells (hHSC) and thymus organoids both of which will be developed from the same HLA-homozygous iPS cells without conditioning by irradiation. This humanized mouse can have osteoclasts differentiated from monocyte linage cells derived from hHSC. We hypothesize that Porphyromonas gingivalis (Pg)-mediated upregulation of Sema4D expressed by human OCs, but not T cells, promotes pathogenic bone resorption and inflammation, but suppresses OB-genesis in periodontitis induced in humanized mice. Aforementioned hypothesis will be tested by following two aims: 1) To profile immune compartments and OCs of human origins in humanized NSG-SGM3-W41 mice which are induced of periodontitis, and 2) To establish the roles of Sema4D released from human OCs in promoting periodontal bone loss and suppressing OB-genesis using a humanized mouse model of periodontitis. Because periodontal bone loss induced in rodents is spontaneously regenerated after the removal of inflammatory stimuli, it has been argued that rodents may not be appropriate models for human periodontitis. However, we for the first time developed and published irreversible bone loss induced in mice by live Pg-soaked ligature attachment. To discriminate the possible engagement of Sema4D produced by platelets, T cells and OCs, using a liposome-clodronate protocol that depletes human platelets, T cells and mouse monocyte lineage cells (including osteoclasts), we will evaluate the periodontal bone outcomes from the Sema4D increased on the human OCs in humanized NSG-SGM3-W41 mice in the absence of mouse OCs. This humanized mouse model of periodontitis would allow us to investigate the interaction between the human host immune system and human periodontal pathogens, such as Pg, in the physiological context. A humanized mouse model of periodontitis would also provide a platform for understanding the susceptibility of individuals to develop a particular systemic disease and support preclinical examinations of precision medicine. Upon our successful completion of this proposed study, it is anticipated that the roles of human Sema4D produced by human osteoclasts, in comparison to that produced by T cells and platelets, in periodontitis will be characterized. In sum, the proposed humanized mouse model of periodontitis has potential to be the next generation biological tool for pathophysiological and pharmacological studies of periodontitis.